Surgical manipulation of the labyrinth has traditionally been avoided out of fear of creating irreversible sensorineural hearing loss. However, recent surgical reports indicate that, under certain conditions, the vestibular labyrinth may be selectively ablated with preservation of hearing. Our long-term goal is to define the surgical conditions that allow hearing to be preserved. In preliminary experiments, using a guinea pig model, we used click- evoked auditory brainstem responses (ABR) to measure hearing thresholds. We found that transection of one or more semicircular canals resulted in preservation of hearing. Intentional suctioning of inner ear fluid caused transient hearing loss with eventual recovery. Progressive transection of a semicircular canal led to preservation of hearing until the ampulla was removed. Wide vestibulotomy led to permanent, incomplete loss of hearing. Our specific aim in this study will be to determine the effect of partial destruction of the labyrinth on high-frequency auditory function using tone-pip ABR. Click-evoked ABR uses a broad-band stimulus that cannot detect frequency-specific losses. Tone-pip ABR allows the measurement of hearing thresholds across frequencies. We plan to obtain special equipment designed to produce high-frequency tone-bursts, which reflect the hearing emphasis of the guinea pig. We anticipate that this work will have considerable potential in neurotologic surgery. Partial labyrinthine destruction with hearing preservation may have two important applications: in surgery for balance disorders, for which current ablative options either sacrifice hearing (labyrinthectomy) or require a formidable intracranial approach (vestibular nerve section); and in tumors of the cranial base, for which conventional surgical approaches often result in hearing loss. The acceptable limits of selective destruction of the labyrinth remain to be defined, and the proposed study is designed to provide an important step in this direction.